New York: In a large new study of older Americans, researchers find that people with the healthiest eating habits are about 15 percent less likely to develop pancreatic cancer than those with the poorest diets.
In the analysis of data on more than 500,000 Americans over age 50, men in particular, especially those who were overweight or obese, appeared to benefit most from a high quality diet.
"It is important to note that our findings are based on overall diet and not individual foods. A combination of many foods contributed to the observed association between greater compliance with the Dietary Guidelines and lower risk of pancreatic cancer," lead author Hannah Arem of the National Cancer Institute in Bethesda, Maryland, told Reuters Health in an email.
Though pancreatic cancer is rare - about 1.5 percent of Americans will develop the disease during their lifetimes - it is one of the most aggressive and lethal cancers. Only about six percent of people with pancreatic cancer are still alive five years after diagnosis, according to Arem.
Past studies looking at the relationship between diet and risk for pancreatic cancer have tended to focus on individual foods and found few connections, according to her team's report, published in the Journal of the National Cancer Institute.
To examine links between overall diet and cancer risk, Arem and her colleagues used the government-designed Healthy Eating Index published in 2005 (HEI-2005) as a basis for rating the overall quality of people's diets.
They applied those criteria to responses from 537,218 men and women who were part of the American Association for Retired Persons Diet and Health Study. Between 1995 and 1996, participants filled out diet questionnaires about how often they ate items on a list of 124 foods.
Arem's team then divided participants into five groups based on how closely their diets met HEI-2005 recommendations for consuming healthy foods such as fruits, vegetables and whole grains and limiting unhealthy ones, like red meat and junk foods.
Scores on the index range from 0 (no guidelines met) to 100 (all guidelines met), with high scores indicating the healthiest eating patterns.
Using state cancer registries and Social Security Administration data, the researchers followed participants for about 10 years and found that 2,383 people developed pancreatic cancer.
About 22 percent of the pancreatic cancer cases were among people with the lowest HEI-2005 scores, while 19 percent were in people with the highest scores. Overall, that translates to a 15 percent lower risk among those with the healthiest diets.
Among men who were overweight or obese, however, those with healthy eating scores in the top-fifth group were 28 percent less likely than their counterparts in the bottom-fifth to develop pancreatic cancer. The same effect was not seen among overweight women.
When the researchers adjusted for other factors linked to pancreatic cancer risk, including smoking, alcohol consumption and diabetes, the effects of diet quality remained the same.
Arem's team also looked at specific subgroups of foods and found that people who ate the greatest amounts of certain healthy foods, such as dark-green and orange vegetables, legumes, whole grains and low-fat milk had lowered risk for pancreatic cancer.
The researchers point out in their report, though, that other recent reviews of the literature have not found similar results for people who ate lots of fruits and vegetables, for example.
"Our study showed an association between diet and pancreatic cancer risk, rather than cause and effect. In general, maintaining a healthy diet has many health benefits," Arem said.
Dr. Rachel Ballard-Barbash, also of the National Cancer Institute, and her colleagues also note in an editorial accompanying the new study that attempts to link individual foods or nutrients to cancer risk have yielded conflicting results.
While some understanding about the relationship between diet and certain cancers has been gained, that "knowledge has not yet translated into noticeable reductions in the incidence of the major cancers with diet-related etiology," they write.
Dr. Alfred Neugut, who studies digestive cancers and epidemiology but was not involved in the current research, agreed there are still a lot of unknowns about the links between diet and cancer.
"If you go out of your way to have a healthy diet, then you're probably going out of your way to be healthy in other ways," Neugut, a professor of medicine at Columbia Presbyterian Medical Center in New York, told Reuters Health. So it's difficult to tease out whether it's really the diet alone that explains the decreased risk seen in the new study.
"It's always safe to say that it's prudent to eat a healthy diet," he said. But, he added, "I would say that diet and cancer is a topic that, despite huge numbers of studies and huge amounts of money invested, has eluded any dramatic findings."